Trunk circuit



R. B. CURTIS April l, 1952 TRUNKl CIRCUIT Filed Obt. 51, 1950 ATTORNEY Patented Apr. 1, 1952 TRUNK CIRCUIT Robert B. Curtis, Bethlehem, Pa., assigner to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application Gctober 31, 1950, Serial No. 193,263

6 Claims.

This invention relates to telephone systems and hasior its object to facilitate supervision between oflices of different types.

More and more toll trunks and switching equipment are of the four-wire type, such as shown in Patent 2,382,893 to McKim and Myers, August 14, 1945, while local trunks and switching equipment are of the two-wire type. Since tandem exchanges are chiefly used in interconnecting local oices, the switching equipment at such exchanges is also of the two-wire type. Therefore, when a call must be extended from a fourwire toll oice through a tandem office to a local oiice, a special type of trunk circuit is required to connect the toll oiiice with the tandem oiiice, which may conveniently be located at the tandem oice.

In accordance with the present invention a trunk circuit for connecting a four-wire trunk with a two-wire trunk is provided with a hybrid coil for constituting a talking connection between the trunks, an incoming supervisory relay and an outgoing supervisory relay, the hybrid coil being normally connected only to the incoming supervisory relay, but connected to 'both super* visory relays during conversation.

The hybrid coil has a set of incoming windings and a set of outgoing windings, both sets being connected to the incoming trunk and incoming supervisory relay when the trunk is idle and means is provided when the trunk is made ready for conversation to switch the outgoing set of windings to the outgoing trunk and outgoing supervisory relay.

These and other features of the invention will be 'more readily understood from the following description taken in connection with the drawing which shows a trunk circuit embodying the invention.V For a disclosure of a tandem sender suitable for use with this trunk circuit reference may be made to Patent 2,281,636 to W. B. Strick 1er, May 5, 1942.

` At the left of the drawing is shown hybrid coil |00, having four incoming windings |05, |06, |I3 and H4, four outgoing windings |08, |09, III and l |2, and two balancing windings |31 and l0. Windings |05 to |09 are wound to constitute one transformer A while windings l I0 to I4 are wound to constitute a second transformer B.

lWhen the incoming sender at the toll oiiice is connected to the outgoing toll trunk circuit at theoutgoing end of the incoming tandem trunk under consideration, the outgoing toll trunk, in response to signals from the toll sender, connects, inv eiect. its polar supervisory relay from conductor I0| and |02 in parallel to conductors |03 and |04 in parallel. A circuit is thereby completed from ground through the lower winding of incoming supervisory relay AR over contact |0 of relay T, contact l2 of relay DI, conductor H8, outgoing windings |00 and H2 of coil |00, contact 5 o1- relay DE, contact of jack TJ, incoming winding H16 of coil |00 and conductor |01 in parallel with incoming winding |05 of coil |00 and conductor |02, polar supervisory relay in outgoing toll trunk circuit, conductors m3 and |04 in parallel through incoming windings H4 and H3 of hybrid coil |90, contact 2 of jack TJ, contact I3 of relay DI, outgoing windings and |08 of coil |00, conductor Ill, contact 3 of relay DI, contact 2 of relay T, through the upper wind-Y ing of incoming supervisory relay AR to battery.

Relay AR operates in this circuit closing a circuit from ground over its contact, contact of relay D contact 'l of relay D2 to start conductor ||5 leading to the sender link |30 which functions to select an idle tandem sender |3| and connect it with the trunk circuit.

. When the sender |3| is attached to the trunk it connects ground to conductor Ei', operating relay T, and connects battery and ground to conductors ||l and H8. Relay T, when operated, disconnects relay AR from the incoming trunk, placing the trunk under the control of the sender. .At the toll oice, the incoming sender responds to the completion of the circuits for relay AR to prepare for sending out multifrequency pulses. The connection of battery and ground to con ductors and H3 by the tandem sender |3| maintains the toll sender in this condition.

When the tandem sender |3| is ready to receive pulses, it reverses the connection of battery and ground'to conductors I |l and H8 as a signal to the toll sender which now proceeds to send out the multifrequency pulses representing the digits of the designation of the wanted line. These digits are registered in the tandem sender |3I. Following the registration of the rst two or three digits, the tandem sender |3| calls in a tandem marker |32 which, in turn, seizes the trunk frame having access to the desired outgoing trunks. The marker then seizes the trunk link and connector frame associated with this trunk and causes the sender |3| to connect ground to conductor vThe connection ci ground to conductor H9 completes'a circuit over contact 6 of relay DI, to battery through the winding oi relay F. Relay F' operates and extends its operating ground over itscontact 3 to conductor |29, leading tothe trunk link connector and thence to the marker as an indication that the connection between the trunk and the marker has been completed. Relay F also connects ground over its contacts 6 and to conductors |2| and |22 to operate the select magnets of the trunk switch. In addition at contact 2 it connects conductor |23 leading to the sleeve contact of the trunk switch to conductor |24 to permit the marker to test the connection with the outgoing trunk after it has been established. When the marker has completed its functions, relay F is released and ground is connected over contact 6 of relay T and contact l of relay F to conductor 23 to hold the switches connecting this trunk with the outgoing trunk.

After the outgoing connection has been established the designation is transmitted to the local oice over conductors |25 and |25.

When the transmission of the designation has been completed, the tandem sender |3| connects ground to conductor |27, completing a circuit over contact of relay F to battery through the winding of relay D. Relay D operates and in turn operates relay DI. At its contact l, relay D disconnects the start conductor ||5 from the contact of relay AR.

Relay DI, in operating, at its contact S connects ground to conductor |23, at its Contact 5 opens the circuit over which relay F was operated and, at its contact closes a circuit from ground at contact 2 of relay D2, contact 8 of relay T, contact l of relay Dl to conductor lli.' as an indication that the transmission circuit has been closed, to which indication the tandem sender |3| responds by disconnecting ground from conductor IIS, permitting relay T to release.

With relay T released, incoming conductors |0| a .d |02 are connected through input windings |85 and |65 of hybrid coil |39 in parallel, contact of jack TJ, contact 4 of relay Dl, contact 2 of relay T, upper winding of relay AR to battery. Conductors |93 and l are connected through input windings lill and ||3 of hybrid coil |02 in parallel, Contact 2 of jack TJ, contact of relay Dl, contact lll of relay T, lower winding of relay AR to ground. Relay AR new operates through the input windings of hybrid coil |00 and closes a locking circuit for relay D.

With relays D and Di operated, outgoing conductor is connected over contact 2 cf relay Dl, output windings lilo and H2 of hybrid coil I, windinsy of outgoing supervisory relay CS, contact I4 of relay Dl, output windings i and |68 of hybrid coil Idil, contact 3 of relay D to outgoing conductor l. However, relay CS is polarized and the initial flow of current in this circuit is in the non-operate direction.

The release of relay T also removes ground from conductor H9, causing the sender link to release and disconnect sender |.3| from the trunk. In addition, relay T released closes a circuit from ground over its contact 1, contact 9 of relay Dl to battery through the winding of relay D2.

Relay D2 operates and closes a locking circuit for itself at its Contact 3 under the control of relay Di but independent of relay T. Relay D2 also connects ground over its contact to conductor |23.

When the connection is completed at the local oiiice and the called subscriber answers, the direction of current ilow in the circuitV of relay CS is reversed and that relay operates. With relay CS operated a circuit is closed from ground at the contact of relay AR, contact 4 of relay T,

Contact of relay CS, contact 5 of relay D2 to battery through the winding of relay T. Relay T operates and locks to ground at its contact 5 independent of relay AR.

With relay T operated the circuit over conductors lill and |02 extends as above traced to contact 4 of relay D| and thence over contact 6 of relay D2 and contact 9 of relay T to the lower winding of relay AR and ground, while the circuit over conductors |03 and IM extends as above traced to contact of relay D| and thence over contact 4 of relay D2, contact 3 of relay T, to the upper winding of relay AR and battery. Therefore, the connection of battery and ground to the toll trunk supervisory circuit is reversed to indicate to the toll oiTice that the call has been answered. The talking currents are transmitted from the incoming trunk to the outgoing trunk by means of the transformers A and B which make up the hybrid coil |00.

if the called line is busy, relay CS is operated intermittently and relayT operates and releases, to repeatedly reverse the connection of battery and ground to the incoming supervisory circuit.

When the called subscriber disconnects at the end of the conversation, relay CS releases in turn releasing relay T to restore the connection of battery and ground to the incoming trunk conductors as a release signal.

When disconnection takes plate at the toll ofnce, relay AR releases, in turn releasing relays D1 DI and D2. The release of relay D2 releases relay T if that relay is still operated, restoring the trunk circuit to normal. Relay D2 is slow to release so that the outgoing trunk conductors will be opened at contacts of relay DI before ground is removed from conductor |23 to release the trunk switches.

What is claimed is:

l. In a telephone system, a trunk circuit, a fourwire trunk incoming to said trunk circuit, a twowire trunk outgoing from said trunk circuit, a hybrid coil for constituting a talking connection between said incoming trunk and said outgoing trunk, said hybrid coil having a set of incoming windings, a set of outgoing windings and a set of balancing windings, an incoming supervisory relay, an outgoing supervisory relay, means for normally connectingsaid incoming trunk through said incoming and outgoing windings to said incoming supervisory relay, and means for connecting said incoming trunk to said incoming supervisory relay independent of said outgoing windings and for connecting said outgoing windings to said outgoing trunk and said outgoing supervisory relay.

2. In a telephone system, a trunk circuit, a four-wire trunk incoming to said trunk circuit, a two-wire trunk outgoing from said trunk circuit, a hybrid coil for constituting a talking connection between said incoming trunk and said-outgoing trunk, said hybrid coil having a. set ofincoming windings, a set of outgoing windings and a set of balancing windings, a metallic supervisory circuit for said incoming trunk normally established through said incoming windings and said outgoing windings, and means for modifying said incoming trunk supervisory circuit to include said incoming windings only and to establish a second metallic supervisory circuit from said outgoing trunk including said outgoing windings only.

3. In a telephone system, a trunk circuit, a four-wire trunk incoming to said trunk circuit, a two-wire trunk outgoing from said trunk circuit, a hybrid coil for constituting a talking connection between said incoming trunk and said outgoing trunk, said hybrid coil having a set of incoming windings, a set of outgoing windings and a set of balancing windings, an incoming supervisory relay, an outgoing supervisory relay, means for normally connecting said incoming trunk through said incoming ,and outgoing windings to said incoming supervisory relay, registering devices, means under the control of said incoming supervisory relay to connect said incoming trunk with one of said registering devices, means responsive to said connection to disconnect said incoming supervisory relay from said incoming trunk, and means under the control of said registering device for connecting said incoming trunk to said incoming supervisory relay independent of said outgoing windings, for connecting saldoutgoing windings to said outgoing trunk and said outgoing supervisory relay and to disconnectsaid registering device.

4. ln a telephone system, a trunk circuit, a fourwire trunk incoming tol said trunk circuit, a twowire truns` outgoing from said trunk circuit, a hybrid coil for constituting a talking connection between said incoming trunk and said outgoing trunk, said hybrid coil having a set of incoming windings, a set of outgoing windings and a set of balancing windings, a'metallic supervisory circuit for said incoming trunk normally established through said incoming windings and said outgo ing windings, registering devices, means controlled over said incoming trunk supervisory circuit to connect said incoming trunk with one of said registering devices, andmeans under the control of said registering device for modifying said incoming trunk supervisory circuit to include said incoming windings only, to establish a second metallic supervisory circuit from said outgoing trunk including said outgoing windings only and to disconnect said registering device.

5. In a telephoning system, a trunk circuit, a four-wire trunk incoming to said trunkl circuit, a two-wire trunk outgoing from said trunk circuit, a hybrid coil for constituting a talking connec tion between said incoming trunk andjsaid out going trunk. said hybrid coil having a `set of incoming windings, a set of outgoing windings and a set of balancing windings, an incoming superifi visory relay, an outgoing supervisory relay, means for normally connecting said incoming trunk through said incoming and outgoing windings to said incoming supervisory relay, registering devices, ineans under the control of said incoming supervisory relay to connect said incoming trunk with one of said registering devices through said incoming windings and said outgoing windings, means responsive to said connection to disconnect said incoming supervisory relay from said incoming trunk, and means under the control of said registering device for connecting said incoming trunk to said incoming supervisory relay independent oi said outgoing windings, for connect'- ing said outgoing windings to said outgoing trunk and said outgoing supervisory relay and to disconnect said registering device.

6. In a telephone system, a trunk circuit, a four-wire trunk incoming to said trunk circuit, a two-wire trunk outgoing from said trunk circuit, a hybrid coil for consituting a talking connection between said incoming trunk and said outgoing trunk, said hybrid coil having a set ci incoming windings, a set of outgoing windings and a set of balancing windings, a metallic supervisory circuit for said incoming trunk normally established through said incoming windings and said outgoing windings, registering devices, means controlled over said incoming trunk supervisory circuit to connect said incoming trunk supervisory circuit with one of said registering devices, and means under the control of said registering device for modifying said incoming trunk supervisory circuit to include said incoming windings only, to establish a second metallic supervisory circuit from said outgoing trunk including said outgoing windings only and to disconnect said registering device.

ROBERT B. CURTIS.

Name Date Pfleiderer Jan. 24, 1939 Number 

